Prior art is limited to Canada balsam in stick form. The stick is held next to a flame, and the balsam melts and flows down over the specimen.
The Canada balsam wafer is placed on top of the specimen in recessed compartments in the slide, and the slide is heated on an electric hot plate. The advantage of using wafers is that the quantity of balsam needed to cover the specimen is predetermined. Also, the use of a hot plate means that many specimens can be sealed during one operation.